$ npx prettier --write test.json  # 通常は.prettierrcの設定で実行
test.json 27ms
$ cat test.json  # インデントは2
  "a": 0

$ npx prettier --tab-width 4 --write test.json  # --tab-widthでインデント幅を指定
test.json 22ms
$ cat test.json  # インデントは4(.prettierrcの設定より優先される)
    "a": 0


指定できるフォーマットオプションは--helpオプションで表示されるFormat optionsで確認することができます。

$ npx prettier --help
Format options:

  --arrow-parens <always|avoid>
                           Include parentheses around a sole arrow function parameter.
                           Defaults to always.
  --bracket-same-line      Put > of opening tags on the last line instead of on a new line.
                           Defaults to false.
  --no-bracket-spacing     Do not print spaces between brackets.
  --embedded-language-formatting <auto|off>
                           Control how Prettier formats quoted code embedded in the file.
                           Defaults to auto.
  --end-of-line <lf|crlf|cr|auto>
                           Which end of line characters to apply.
                           Defaults to lf.
  --html-whitespace-sensitivity <css|strict|ignore>
                           How to handle whitespaces in HTML.
                           Defaults to css.
  --jsx-single-quote       Use single quotes in JSX.
                           Defaults to false.
  --parser <flow|babel|babel-flow|babel-ts|typescript|espree|meriyah|css|less|scss|json|json5|json-stringify|graphql|markdown|mdx|vue|yaml|glimmer|html|angular|lwc>
                           Which parser to use.
  --print-width       The line length where Prettier will try wrap.
                           Defaults to 80.
  --prose-wrap <always|never|preserve>
                           How to wrap prose.
                           Defaults to preserve.
  --quote-props <as-needed|consistent|preserve>
                           Change when properties in objects are quoted.
                           Defaults to as-needed.
  --no-semi                Do not print semicolons, except at the beginning of lines which may need them.
  --single-quote           Use single quotes instead of double quotes.
                           Defaults to false.
  --tab-width         Number of spaces per indentation level.
                           Defaults to 2.
  --trailing-comma <es5|none|all>
                           Print trailing commas wherever possible when multi-line.
                           Defaults to es5.
  --use-tabs               Indent with tabs instead of spaces.
                           Defaults to false.
                           Indent script and style tags in Vue files.
                           Defaults to false.